1. Field of the Invention
The present invention relates to a super conducting quantum interference device (SQUID), more particularly, it relates to a digital SQUID control system used for a magnetic flux meter for measuring a weak magnetic flux irradiated from an object to be measured.
2. Description of the Related Art
SQUID's are utilized for detecting a weak magnetic flux with very high sensitivity. That is, the SQUID can respond to a change in a weak magnetic flux based on the quantum interference effect of the magnetic flux. Accordingly, the SQUID is mainly utilized for, particularly, a high sensitivity magnetic flux meter having a highly sensitive magnetic sensor. The high sensitivity magnetic flux meter is utilized, for example, in the field of medical equipment to measure the magnetic flux from a human body.
In general, the SQUID can be classified into two types, i.e., an analog type SQUID and a digital type SQUID. Both analog and digital types have two Josephson junctions and a superconductivity coil. The present invention relates to a digital type SQUID.
The high sensitivity magnetic flux meter utilizing the SQUID includes a SQUID, a pick-up coil detecting the magnetic flux from an object and magnetically coupled to the SQUID, and a feedback circuit supplying a control current to a feedback coil also magnetically coupled to the SQUID.